Medium Modification of γ Jets in High-Energy Heavy-Ion Collisions

Two puzzling features in the experimental study of jet quenching in central Pb + Pb collisions at the LHC are explained within a linearized Boltzmann transport model for jet propagation. A gamma-tagged jet is found to lose about 15% of its initial energy while its azimuthal angle remains almost unchanged due to rapid cooling of the medium. The reconstructed jet fragmentation function is found to have some modest enhancement at both small and large fractional momenta as compared to that in the vacuum because of the increased contribution of leading particles to the reconstructed jet energy and induced gluon radiation and recoiled partons. A gamma-tagged jet fragmentation function is proposed that is more sensitive to jet-medium interaction and the jet transport parameter in the medium. The effects of recoiled medium partons on the reconstructed jets are also discussed.